Keysight CXG, EXG, and MXG X-Series Signal Generators Service Guide 131
Troubleshooting
Unlocked Issues
Internal Reference Unlocked
Use the following procedure to troubleshoot a 512 Reference Unlocked error
when using the internal frequency reference oscillator:
1. Disconnect any cable attached to the REF IN port on the rear panel of the
instrument.
2. Force the instrument to use the internal reference by pressing FREQ, More,
Reference Oscillator, Ref Oscillator Source, Int.
3. If the unlock persists verify that there is no user reference tuning that is
affecting it by pressing Utility, Instrument Adjustments, Ref Oscillator
Tune and setting it to 0.
4. If the unlock persists run the following instrument adjustments:
— Reference VCO Tank DAC Calibration
— Reference Internal Standard Calibration
— Reference VCO Kv Calibration
5. If the unlock persists, replace the A3 RF assembly.
External Reference Unlocked
Use the following procedure to troubleshoot a 512 Reference Unlocked error
when using an external frequency reference:
1. Connect a 10 MHz signal with a power level of 0 dBm to the REF IN port on
the rear panel of the instrument. (The power level of the external reference
should be between -3 dBm and +20 dBm.)
2. Force the instrument to use the external reference by pressing FREQ,
More, Reference Oscillator, Ref Oscillator Source, Ext.
3. If the instrument has option 1ER, flexible reference input, verify that the
FREQ, More, Reference Oscillator, Ref Oscillator Ext Freq setting is set to
10 MHz.
4. If the unlock persists, replace the A3 RF assembly.
508 Synthesizer Unlocked
This type of an unlock indicates that one of the phase lock loops in the
synthesizer section of the A3 RF assembly is unlocked. While the CXG and EXG
series instruments have only one phase lock loop in the synthesizer section,
the MXG instruments have three.
The 100 MHz VCXO provides a reference for the phase lock loop in the CXG
and EXG series and the initial FracN loop for the MXG series. If the 100 MHz
reference phase lock loop is unlocked, a properly functioning synthesizer phase
lock loop should be able to remain locked, as it should have enough range to
lock to the 100 MHz reference signal at the extremes of it tunable range.
However, a non-functioning 100 MHz reference could cause the synthesizer
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